Sulfonic acid-containing binding agent for moulding mixes for the preparation of moulds and cores

ABSTRACT

A polyisocyanate component for a moulding material binding agent system is described containing at feast one sulfonic acid in a solution of at least one polyisocyanate, containing at least two NCO-groups in the molecule.

The invention relates to a polyisocyanate component for a moulding material binding agent system or a solution containing polyisocyanate for a moulding material binding agent system or a two-component binding agent system, the use of these for the production of foundry sand cores or moulds according to the cold-box method, corresponding foundry moulding materials and foundry sand cores or moulds and the preparation of these and the use of particular sulfonic acids as a means for extending the benchlife.

In the preparation of foundry sand cores and moulds the polyurethane-forming cold-curing binding agent systems are of great importance. These binding agent systems consist of two components, a polyol (normally dissolved in a solvent) with at least two OH-groups in the molecule and a polyisocyanate (usually likewise dissolved in a solvent) with at least two NCO-groups in the molecule. Both components which are added separately to the moulding mixes containing a moulding matrix, preferably sand, react in the moulding mix to form a cured polyurethane binding agent, typically in the presence of catalysts, which guarantee a rapid reaction and thus a sufficiently short curing time. In addition to other substances such as metal-organic compounds, in the main tertiary amines are considered as catalysts which after moulding of the moulding mix are introduced into the moulding tool as highly volatile amines with a carrier gas.

The polyol component is usually a condensation product of (possibly substituted) phenols with aldehydes (hereinafter referred to as “phenolic resin” for short) dissolved in a solvent, having a low-to-average degree of condensation and a large number of free OH-groups in the molecule. In certain cases, in particular with sand cores for low casting temperatures, the polyol component, however, can also be a solution of an oligomeric, dimeric or monomelic phenol body, e.g. of a terphenol, bisphenol or dihydroxybenzol. For all these polyois a large number of (generally polar) solvents are available. The solutions are normally set at a solid content of 40 to 95 wt. % and can further contain normal additives.

In principle all polyisocyanates with at least two NCO-groups in the molecule can be considered as polyisocyanate components. Preference is for aromatic polyisocyanates, of which diphenylmethane-4,4′-diisocyanate, 2,2′,6,6′tetramethyldiphenylmethane-4,4′-diisocyanate, diphenyldimethylmethane-4,4′-diisocyanate and diphenyl-4,4′-diisocyanate are typical examples. The polyisocyanates can form the polyisocyanate component either in pure form or dissolved in an organic solvent, e.g. a mixture of aromatic hydrocarbons with a boiling point of above 150° C. In the case of a solution the concentration of the polyisocyanate is generally above 70 wt. %.

For the preparation of a moulding mix a moulding matrix, preferably a grainy moulding sand such a quarto sand, chromite sand, olivine sand, or zircon sand, is mixed with the two binding agent components, wherein the proportions of the two components can be approximately in the region of 0.5 to 1.5 parts by weight of polyisocyanate component to 1 part by weight of polyol component and preferably can be dimensioned such that an almost stoichiometric ratio of the NCO-groups to the OH-groups results. The moulding mix is then processed to form the foundry sand cores or moulds, e.g. in that they are filled or fired into a moulding tool, possibly compressed and then cured by a short period of gasification with a highly volatile tertiary amine such as dimethyethylamine or trimethylamine. The sand cores or moulds can then be removed from the moulding tool.

In the course of gasification the sand cores or moulds will already achieve a measurable strength (“initial strength”), which upon completion of the gasification increases slowly to reach the final strength value. In practice the highest possible initial strength is desirable here, in order that the sand cores or moulds as far as possible can be removed from the moulding fool immediately after gasification and the tool can be freed up for another work cycle.

Sufficiently high initial strengths can be achieved with binding agent systems adjusted to be reactive. However, excessive reactivity of the system has the result that the period for which the moulding mix mixed from the two binding agent components can be stored before being further processed into sand cores or moulds (the so-called “benchlife”), is as significantly shortened. This is a serious disadvantage, for there is a practical requirement for sufficient benchlives, so that a prepared charge of a moulding mix (moulding sand mixture) does not become prematurely unusable. Good benchlives are provided by less strongly reactive binding agent systems, but these in turn result in poorer initial strengths.

In order to be able to meet the dual requirements of the highest possible initial strength and the best possible benchlife, phosphoryl chloride, phthaloyl chloride or chlorosilanes are added to the polyisocyanate component of the binding agent. DE-A-34 05 180 describes such a moulding material binding agent system containing chlorosilanes.

Binding agent systems containing acid chlorides are known from U.S. Pat. No. 4,540,724.

The chlorine content of the binding agent system can lead to disadvantages and health risks during the processing of the binding agent system and the subsequent metal casting, since as the binding agent system decomposes, chlorinated compounds, such as dioxins, which are a health hazard, can result. Thus there is a need for a substitute for acid chlorides or chlorosilanes, which can extend the benchlife of a moulding material and which is at the same time chlorine-free. The substitute should be capable of fully or partially replacing the acid chlorides or chlorosilanes used to date, without adversely affecting the benchlife or the strength of the sand cores (initial strength and final strength).

The object of the present invention is to provide a corresponding chlorine-free substitute which meets the above requirements.

DE 2921726 discloses special emulsions containing water, an organic polyisocyanate, possibly a non-ionic, surface-active medium as an emulsifier and a sulfonic acid. Here the sulfonic acid is a sulfonic acid of the general formula R—(SO₃H)_(n), in which n denotes an integer 1 or 2 and R an aromatic hydrocarbon radical with 6 to 14 carbon atoms, an aliphatic hydrocarbon radical with 10 to 18 carbon atoms, a cycloaliphatic hydrocarbon radical with 6 to 15 carbon atoms, an araliphatic hydrocarbon radical with 7 to 15 carbon atoms or an alkaramatic hydrocarbon radical with 7 to 24 carbon atoms.

DE 2921698 A1 discloses a self-releasing, substantially anhydrous, polyisocyanate-based binding agent for the production of moulded forms consisting of

-   A) a polyisocyanate and -   B) a sulfonic acid of the general formula R—(SO₃H)_(n), in which     -   n denotes an integer 1 or 2 and     -   R an aromatic hydrocarbon radical with 6 to 14 carbon atoms, an         aliphatic hydrocarbon radical with 10 to 18 carbon atoms, a         cycloaliphatic hydrocarbon radical with 6 to 15 carbon atoms, an         araliphatic hydrocarbon radical with 7 to 15 carbon atoms or an         alkaromatic hydrocarbon radical with 7 to 24 carbon atoms,         wherein the equivalent ratio of components A) and B) is between         100:0.5 and 100:20.

JP 03-041116 concerns certain polyurethane resin compositions for orthopedic cast strips comprising a polyurethane prepolymer comprising a polyol and a polyisocyanate, a catalyst a stabiliser (e.g. acid chlorides such as benzoyl chloride or sulfonic acids such as methane sulfonic acid) and an ester compound polyethylene glycol.

DE 4213873 describes the use of esters that are liquid at ambient temperature as a solvent for isocyanates and/or isocyanurates, whereby the viscosity of the isocyanates and/or isocyanurates can be drastically reduced.

DE 19542752 describes the use of vegetable oil methyl ester, preferably of rapeseed oil methyl ester, as a solvent for individual or both components of foundry moulding material binding agents with a polyurethane basis, the components of which comprise a phenolic resin containing free OH-groups and a polyisocyanate as the reaction partner.

JP 53-128526 discloses how, for the preparation of a self-curing mould mixture, a phenolic resin containing 0.05 to 40% carboxylic and/or sulfonic acid and sand is mixed with a polyisocyanate in the presence of a basic catalyst.

JP 62-104648 discloses how, for the preparation of a sand mould, foundry sand is kneaded with a binding agent comprising a furan resin, toluenesulfonic acid, tetraethylsilicate, methyl diisocyanate, silicon dioxide and boric acid.

CN 102049463 discloses a method comprising the mixing of a sodium alkyl sulfonate solution with a phenolic resin, and then mixing with sand, further mixing with a polyisocyanate-ester, and the moulding of a casting mould.

The object posed is achieved according to the invention by the use of a sulfonic acid of the general formula R—SO₂—OH, in which R denotes C₁₋₄-alkyl, preferably methyl, as a means to extend the benchlife of a mixture, comprising

-   -   a moulding matrix, preferably a moulding sand,         and     -   the polyisocyanate component and the polyol component of a         two-component binding agent system for preparation of a         polyurethane resin for casting, preferably according to the         polyurethane cold-box method,         wherein         the polyisocyanate component comprises one or a plurality of         polyisocyanates with in each case two or more NCO-groups in the         molecule, wherein the one polyisocyanate or at least one of the         plurality of polyisocyanates is a methylene diphenyl         diisocyanate or an oligomer or polymer thereof,         and wherein         the polyol component preferably comprises a phenol-formaldehyde         resin with two or more methylol groups per molecule,         particularly preferably a benzyl ether resin with ortho-ortho         structures.

Further aspects of the present invention are apparent from the attached claims and the following description.

According to the invention it has been discovered that the sulfonic acids to be used according to the invention can be used to extend the benchlife of a moulding material and in so doing can replace in full or in part the known chlorosilanes or acid chlorides.

The invention therefore also relates to (i) a polyisocyanate component for a moulding material binding agent system, and (ii) a solution containing polyisocyanate (see below).

The invention further relates to a moulding material binding agent system for the preparation of foundry sand cores from a polyol component, containing a solution of a phenol-containing polyol, such as benzyl ether resin with ortho-ortho structures, with at least two OH-groups in the molecule, and a polyisocyanate component, as defined as above, which react with one another to form a cold-curing binding agent, e.g. for sand cores or moulding sand. The invention also relates to a moulding material binding agent system for the preparation of foundry sand cores from

-   -   a polyol component, containing phenol formaldehyde resin, such         as benzyl ether resin with ortho-ortho structures, with at least         two OH-groups in the molecule,         and     -   a polyisocyanate component, as defined above,         which reset with one another to form a cold-curing binding         agent.

The invention also relates to a two-component binding agent system for the preparation of a polyurethane resin for casting (see below).

The invention also relates to the use of a polyisocyanate component or a solution containing polyisocyanate, a moulding material binding agent system according to the invention or a two-component binding agent system according to the invention for the preparation of foundry sand cores according to the cold-box method.

The invention also relates to a mixture for preparation of a core or a mould for casting, e.g. a foundry moulding material, and corresponding foundry sand cores and moulds and a method for the preparation thereof.

The foundry moulding material can also be used as a foundry moulding sand for the preparation of casting moulds, e.g. for the no-bake method.

The invention also relates to a polyisocyanate component for a moulding material binding agent system, containing at least one sulfonic acid in a solution of at least one polyisocyanate, containing at least two NCO-groups in the molecule, characterised in that:

-   -   the sulfonic acid has the general formula R—SO₂—OH, in which R         denotes C₁₋₄-alkyl, preferably methyl,         and     -   the polyisocyanate component contains methylene diphenyl         diisocyanate (MDI) or an oligomer or polymer thereof.

A further subject matter of the invention is a solution containing a polyisocyanate, preferably a polyisocyanate component as defined above, for a moulding material binding agent system, wherein the solution containing polyisocyanate consists of

-   (a) one or a plurality of polyisocyanates with in each case two or     more NCO-groups in the molecule, wherein the one polyisocyanate or     at least one of the plurality of polyisocyanates is a methylene     diphenyl diisocyanate or an oligomer or polymer thereof,     and -   (b) one or a plurality of sulfonic acids, wherein the one sulfonic     acid or at least one of the plurality of sulfonic acids is selected     from the group of sulfonic acids of the formula R—SO₂—OH, in which R     denotes an alkyl group with between 1 and 4 carbon atoms, wherein     preferably the one sulfonic acid or at least one of the plurality of     sulfonic acids, is methane sulfonic acid,     or comprises the components (a) and (b) defined here.

According to the invention preference is for a solution containing polyisocyanate comprising or consisting of

-   (a) one or a plurality of polyisocyanates with in each case two or     more NCO-groups in the molecule, wherein the one polyisocyanate or     at least one of the plurality of polyisocyanates is a methylene     diphenyl diisocyanate or an oligomer or polymer thereof,     and -   (b) one or a plurality of sulfonic acids, wherein the one sulfonic     acid or at least one of the plurality of sulfonic acids is selected     from the group of sulfonic acids of the formula R—SO₂—OH, in which R     denotes an alkyl group with between 1 and 4 carbon atoms, wherein     preferably the one sulfonic acid or at least one of the plurality of     sulfonic acids, is methane sulfonic acid.     and additionally -   (c) one or a plurality of (co)-solvents, not selected from the group     of ingredients (a) and (b) defined above,     and/or -   (d) one or a plurality of further substances selected from the group     consisting of acid chlorides and chlorosilanes     and/or -   (e) one or a plurality of further substances selected from the group     of water repellents.

Here, preference according to the invention is for solutions containing polyisocyanate. which contain no substances (d) selected from the group consisting of acid chlorides and chlorosilanes. Chlorinated compounds may, however, in individual cases, be acceptable in small quantities in the solution containing polyisocyanate according to the invention. Commercial grades of methylene diphenyl diisocyanate (and other polyisocyanates) in particular and their oligomers or polymers comprise certain quantities of chlorinated compounds as an impurity, due to the use of chlorinated educts during synthesis. These chlorinated compounds may be acceptable as an impurity in solutions containing polyisocyanate according to the invention. In order to further reduce the burden from the release of chlorine during the casting process, however, it is preferred, for the preparation of the solution containing polyisocayanate according to the invention, to use polyisocyanate grades in which the chlorinated impurity content is as low as possible, or to reduce the content of such chlorinated impurities in the polyisocyanates to be used as far as possible by suitable purification processes.

The (co-)solvents of component (c) can also be based on commercially available products, which apart from a (preferably chlorine-free) main ingredient also comprise certain quantities of chlorinated compounds as an impurity. In this connection, however, it is preferred, for preparation of the solution containing polyisocyanate according to the invention to use (co-)solvent grades in which the content of chlorinated impurities is as low as possible or to reduce the content of such chlorinated impurities in the (co-)solvents to be used as far as possible by suitable purification processes.

The term (co-)solvent (c) means that the component (c) either acts as a solvent itself, where none of the ingredients of components (a) and (b) themselves act as a solvent for the other ingredients of components (a) and (b), or acts as an additional solvent, where one or a plurality of ingredients of components (a) and (b) itself/themselves acts or act as a solvent for the other ingredients of components (a) and (b).

Aminosilanes and aminoorganosilanes, such as gamma-aminopropyltriethoxysilane, gamma-aminopropyltrimethoxysilane, bis-(gamma-erimethoxysilylpropyl)amine, polyazamidsilane, N-beta(amincethyl)-gamma-aminopropytrimethoxysilane, N-phenyl-gamma-aminopropyltrimethoxysilane, organically modified polydimethoxysiloxsne, and triamino-functional silanes are often used as the water repellent (e).

Here, according to the invention, it is preferred that the solution containing polyisocyanate defined above does not comprise a resin selected from the group consisting of phenolic resins and furan resins.

Particularly preferably according to the invention the solution containing polyisocyanate comprises no polyol that is suitable for reacting with the polyisocyanate(s) contained in the solution to form a cold-curing binding agent.

A solution containing polyisocyanate according to the invention preferably comprises no moulding matrix, in particular no casting sand.

The solution containing polyisocyanate according to the invention is preferably either anhydrous or contains water in a maximum quantity that is selected so that the molar ratio of NCO-groups to H₂O is greater than 100:1, preferably greater than 1000:1.

The polyisocyanate component according to the invention or the solution containing polyisocyanate according to the invention contains one or a plurality of sulfonic acids, wherein the one sulfonic acid or at least one of the plurality of sulfonic acids is selected from the group of sulfonic acids of the formula R—SO₂—OH, in which R denotes an alkyl group with between 1 and 4 carbon atoms, wherein preferably the one sulfonic acid or at least one of the plurality of sulfonic acids, is methane sulfonic acid.

Additionally, the following applies: The sulfonic acid can be selected from any suitable sulfonic adds. Preferably, the sulfonic acid has the general formula R—SO₂—OH, in which R denotes C₁₋₁₂-alkyl, phenyl or C₁₋₁₂-alkylphenyl, wherein an H atom in these radicals can be substituted by a hydroxyl group or amino group, which can be primary, secondary or tertiary, or R denotes NH₂.

The sulfonic acid can be used in pure form or as a solution in a, preferably, organic solvent. Here the sulfonic acid can be present in the form of a free acid or also partly in the form of a salt, for example an ammonium, alkaline or alkaline earth metal salt. The salt content, in respect of the acid groups, should preferably not exceed 30 mol %. Preferably, only the free acid is used.

The use of sulfonic acid leads to a considerable extension of the benchlife, without this being accompanied by a significant drop in strength (initial strength and final strength). This effect is achieved in a range of low added quantities. Preferably, the polyisocyanate component contains 0.01 to 5 wt. %., particularly preferably 0.0025 to 2.5 wt. %., preferably 0.025 to 2.5 wt. %., in particular 0.05 to 1 wt. %, of the minimum of one sulfonic acid, in respect of the polyisocyanate component.

A solution containing polyisocyanate according to the invention (as defined above) preferably comprises a total quantity of sulfonic acid in the range 0.01 to 5 wt. %., in respect of the total weight of the solution.

With the additional use of acid chlorides or chlorosilanes the weight ratio of sulfonic acid to acid chloride or chlorosilane is preferably 1:1 to 9:1, particularly preferably 1:1 to 4:1, in particular approximately 1:1. Preferably no acid chloride or chlorosilane is also used.

Unlike phosphoryl chloride, methane sulfonic acid is an odourless, non-oxidising, biodegradable, non-toxic, aliphatic, thermally resistant, low TOC (Total Organic Compound) and strong organic add. Furthermore, the methane sulfonic acid has an extremely low vapour pressure and is part of the natural sulphur cycle.

Here the polyisocyanate component preferably contains 55 to 85 wt. %, particularly preferably 70 to 90 wt. % of the at least one polyisocyanate. The polyisocyanate component can also contain a solvent, preferably in a quantity of 4.99 to 44.99 wt. %, particularly preferably 9.99 to 29.99 wt. %.

A solution containing polyisocyanate according to the invention (as defined above) preferably comprises a total quantity of polyisocyanate in the range 55 to 95 wt. %., in respect of the total weight of the solution.

Here, the total quantity of the ingredients of the polyisocyanate component or the solution according to the invention comes to 100 wt. %. Preferably the total quantity of polyisocyanate, sulfonic acid and solvent comes to 100 wt. %.

The invention is applicable to all polyurethane-based binding agent systems, and can thus be used in conjunction with all normal polyol components and polyisocyanate components and also requires no changes to the preparation and processing of the moulding mixes (moulding sand mixtures). The optimum quantity of sulfonic acid in each case is dependent here on the nature and reactivity of the polyol component and can be determined in each individual situation through simple manual trials. For suitable polyol components and polyisocyanate components, reference may be made, by way of example, to DE-A-34 05 180. DE-A-10 2004 057 671, EP-A-1 057 557 554, EP-A-0 771 599 and WO 2010/060826. All suitable phenol-formaldehyde resins can be used, with the use of benzyl ether resins being particularly advantageous however.

The polyisocyanate component according to the invention or the solution containing polyisocyanate according to the invention comprises one or a plurality of polyisocyanates with in each case two or more NCO-groups in the molecule, wherein the one polyisocyanate or at least one of the plurality of polyisocyanates is a methylene diphenyl diisocyanate (MDI) or an oligomer or polymer thereof. A mixtures of 4,4′-,2,2′- and 2,4′-isomers may be involved here or individual isomers or mixtures of two of the isomers, or also oligomers or polymers of these. This means that according to the invention use may be made of

-   -   an isomer selected from the group consisting of the 4,4′-, the         2,2′- and 2,4′-isomers of the monomer methylene diphenyl         diisocyanate (MDI),     -   mixtures consisting of or containing two or all isomers of the         monomer methylene diphenyl diisocyanate (MDI),     -   oligomers and polymers of the methylendiphenyldiisocyanate         (MDI),     -   mixtures consisting of or containing two or a plurality of         oligomers and/or polymers of the methylene diphenyl diisocyanate         (MDI),     -   mixtures consisting of or containing one or a plurality of         isomers of the monomer methylene diphenyl diisocyanate (MDI) and         one or a plurality of oligomers and/or one or a plurality of         polymers of the methylene diphenyl diisocyanate (MDI).

The use of oligomers and polymers of the methylene diphenyl diisocyanate (MDI) is preferred according to the invention.

Furthermore, the following applies: Here the polyisocyanate can be selected from any suitable polyisocyanates, which contain at least NCO-groups in the molecule and with a phenol-containing polyol produce a cold-curing binding agent for casting sand. Suitable polyisocyanates are known to a person skilled in the art.

As solvents or co-solvents for the polyisocyanate or the solution according to the invention (as defined above), preferably tetrasilicates such as tetraethyl silicate, aromatic hydrocarbons, fatty acid alkyl esters (preferably rapeseed oil methyl ester), mixtures of these and mixtures of these with alkylene carbonates such as propylene carbonate or dialkyl esters of aliphatic dicarboxylic acids, preferably dimethyl esters of adipinic acid, glutaric acid and/or succinic acid, can be considered. The latter dialkyl esters are for example sold under the designation DBE (Dibasic Ester). They are used as co-solvents. in order to improve the solubility, for example in tetraethyl silicate, aromatic hydrocarbons or rapeseed oil methyl esters.

Alkylene carbonate or DBE are added to the first solvent mentioned preferably in a ratio of weight of 1:1 to 5, preferably 1:1.5 to 3, thus in a clearly low quantity.

The subject matter of the invention is also the use of a polyisocyanate component according to the invention (as defined above) or a solution containing polyisocyanate according to the invention (as defined above) as a polyisocyanate component of a two-component binding agent system for preparation of a polyurethane resin, preferably as a polyisocyanate component of a two-component binding agent system for preparation of a polyurethane resin in the polyurethane cold-box method.

A further subject matter of the present invention is a two-component binding agent system for preparation of a polyurethane resin for casting, consisting of

-   -   a polyisocyanate component according to the invention as defined         above or a solution containing polyisocyanate according to the         invention as defined above as a polyisocyanate component,         and separately     -   a polyol component, wherein the polyol component preferably         comprises a phenol-formaldehyde resin with two or more methylol         groups per molecule, particularly preferably a benzyl ether         resin with ortho-ortho structures.

Phenol-formaldehyde resins are synthetic resins, which are obtained by condensation of phenols with formaldehyde and if necessary by derivatisation of the resultant condensates. Phenol-formaldehyde resins are normally, depending on the proportions of the educts (phenol component and formaldehyde), the reaction conditions and the catalysts used, split into two product classes, the novolacs (phenol novolacs) and resoles:

Here novolacs are soluble, fusible, non-self-curing and stable when stored oligomers with molecular weights in the range of approximately 500 to 5000 g/mol. They are produced by condensing formaldehyde and a phenol component in a molar ratio of approximately 1:1.25 to 2 in the presence of acid catalysts. Novolacs are generally free of methylol groups, and their aromatic rings are linked by methylene bridges. Novolacs can be cured by reactive cross-linkers (curing agents) (e.g. hexamethylene tetramine, formaldehyde, isocyanates such as methylene didiphenyl isocyanate, epoxides etc,) at high temperature with cross-linking. Novolacs are usually insoluble in water.

Resoles are mixtures of hydroxymethyl phenols, linked by methylene and methylene ether bridges. They are prepared by an alkaline catalysed condensation reaction with molar excess of the aldehyde. Once a certain degree of polymerisation has been reached here the condensation is interrupted. Resoles are self-curing through their reactive methylol groups. Depending on the degree of condensation resoles are liquid and as such have different viscosities and are as a rule soluble in water and alcohol. Resoles can be converted into highly cross-linked structures (resites) under the effect of heat. For particular areas of application it is sometimes desirable for resoles to have a certain solubility in organic solvents. In order to achieve this solubility, resoles are then normally subjected to modification reactions, such as for example, condensation at higher temperature with unsaturated compounds (such as for example vegetable oils), esterification or etherification with mono- or polyfunctional alcohols.

A particular class of phenol formaldehyde resins are benzyl ether resins. Benzyl ether resins are the products of condensation of a phenol component and formaldehyde, obtained under the catalytic influence of bivalent metal ions, see U.S. Pat. No. 3,485,797. Benzyl ether resins are particularly suitable as a resin component for casting binding agents for use in the cold-box method (see U.S. Pat. No. 3,676,392 and U.S. Pat. No. 3,409,579). Benzyl ether resins are liquid up to a certain degree of condensation. Benzyl ether resins are as a rule incompatible with wafer, but compatible with alcohols and other organic solvents. The particular feature of benzyl ether resins is their structure. They have phenol bodies which are linked by both methylene groups —CH₂— and by ether groups —CH₂—O—CH₂—, wherein the linking of two bodies takes place predominantly in the ortho-ortho position, in benzyl ether resins there is a high content of hydroxymethyl groups (—CH₂OH) and phenolic hydroxyl groups (—OH). The fact that benzyl ether resins have predominantly o,o-structures (ortho-ortho-structures) and accordingly have a linear molecular structure, makes them highly reactive to cross-linkers (see again U.S. Pat. No. 3,485,797). Their good compatibility with organic solvents is responsible for their particular suitability as a resin component for casting binding agents for use in the cold-box method. Benzyl ether resins usually contain a high concentration of residual monomers (phenol component; formaldehyde) once the condensation reaction is complete. In addition to this benzyl ether resins can only be processed with comparatively high quantities of solvents, which in view of the ever-stricter directives on handling products containing solvents, limits their applicability. The great need for solvents for processing benzyl ether resins is a result of their comparatively high viscosity which as a rule must be lowered by the addition of solvent.

Preferred benzyl ether resins are described in EP-B-1 057 554. Compounds that are preferably used according to the invention are described there in paragraphs [0004] to [10006], wherein particular reference may be made to Formulas I and II given there.

Special phenol-formaldehyde resins with low viscosity are described in particular in DE-A-10 2004 057 671.

According to the invention, the phenol-formaldehyde resins are preferably used as a polyol component and can be termed a phenol-containing polyol. Here the viscosity of she polyol component is in particular 130 to 140 mPa s at 20° C. For this purpose the polyol component can have a solvent, for example in a quantity of 30 to 50 wt. %. Suitable solvents are aromatic and aliphatic hydrocarbons, esters, ketones, alkyl silicates, fatty acid esters and similar solvents. When low-viscosity phenol-formaldehydes according to DE-A-10 2004 057 671 are used the solvent contents can be considerably reduced.

For other polyol components and polyisocyanate components reference may be made to that stated in the introduction to the description. Here both components are used in the proportions referred to there.

The subject matter of the present invention is also the use of a polyisocyanate component according to the invention as defined above or a solution containing polyisocyanate according to the invention as defined above or a two-component binding agent system as defined above

-   -   for the preparation of foundry sand cores or moulds according to         the cold-box method         and/or     -   for preparation of a polyurethane resin preferably using the         polyurethane cold-box method.

A further subject matter of the invention is a mixture for the preparation of a core or a mould for casting, comprising

-   -   a moulding matrix, preferably a moulding sand,         and     -   either the components of a moulding material binding agent         system or the two-components of a two-component binding agent         system according to the invention.

Such mixtures comprising a (I) moulding matrix, wherein the moulding matrix preferably is a moulding sand, and (ii) a binding agent system (in particular the two components of a two-component binding agent system) are in connection with the present invention also referred to as (foundry) moulding materials, moulding mixes or moulding sand mixtures.

Preferably for the preparation of the foundry moulding material 100 parts by weight of sand, for example quartz sand, or another suitable moulding matrix, are mixed with in each case 0.25 to 2 parts by weight, preferably in each case 0.5 to 1.5 parts by weight of the polyol components and the polyisocyanate component. Here mixing preferably takes place at room temperature using normal mixing equipment.

The foundry moulding materials obtained in this way can be used in any suitable method for the preparation of foundry sand cores or moulds.

Other subject matters of the present invention are thus

a mould or a core for casting,

-   -   composing a moulding matrix, preferably a moulding sand, and the         cured binding agent system resulting either from the curing of a         moulding material binding agent system according to the         invention as defined above or the curing of a two-component         binding agent system according to the invention as defined above         or     -   that can be produced by moulding a mixture comprising a moulding         matrix, preferably a moulding sand, and the components of a         moulding material binding agent system according to the         invention, or the components of a two-component binding agent         system according to the invention and curing of the binding         agent system in the moulded mixture to form a cured binding         agent system,         and         a method for preparation of a foundry core or mould, preferably         according to the polyurethane cold-box method, with the         following steps:     -   mixing of a moulding matrix, preferably a moulding sand, with         the components of a moulding matrix binding agent system         according to the invention or with the components of a         two-component binding agent system according to the invention,     -   moulding of the resultant mixture comprising moulding matrix and         the components of the binding agent system.     -   bringing the resultant moulded mixture into contact with a         gaseous catalyst, preferably (in particular in the context of         the cold-box method) with a gaseous amine, so that the binding         agent system cures and binds the moulding matrix.

Preferably the foundry sand cores or moulds are produced according to the cold-box method. In foundries the cold-box method is one of the most important polyurethane gasification methods. The designation is that used by the VDG and has also been introduced into the German casting industry to designate this method. On this point reference may be made to U.S. Pat. No. 3,409,579. In the cold-box method an amine gassing agent such as for example dimethyl isopropylamine serves as an acceleration catalyst, which considerably accelerates the addition of polyisocyanate to a phenolic resin, e.g. benzyl ether resin. In the process a polyurethane is formed. Resins used in the cold-box method are as a rule anhydrous here, since water would react prematurely with the polyisocyanate.

The process normally involves the foundry sand containing the binding agent system according to the invention (core sand) initially being fired into core boxes. Then using an amine-air or amine-nitrogen mixture in gas or aerosol form, it is gasified. The amines involved are generally triethyl-, dimethylethyl-, dimethyl-n-propyl- or dimethylisopropylamine, which are in each case blown into the core boxes at a pressure of 2 to 6 bar. The residual gases are normally driven out of the core with heated scavenging air, nitrogen or CO₂ gas and can be disposed of in an acid scrubber, charged with diluted sulphuric acid or phosphoric acid.

Here the binding agent system according to the invention, depending on the amine, cures at temperatures of preferably 20 to 100° C., particularly preferably 45 to 80° C. In the cold-box method especially, the curing normally takes place at the respective ambient temperature normally prevailing in the foundry, that is to say generally at a temperature in the range 15 to 50° C., in particular at a temperature in the range 15 to 40° C. Therefore the binding agent is referred to as a cold-curing binding agent for moulding sand.

The cold-box method has extensive applications, in particular in metal casting and for example in engine castings.

The moulding materials according to the invention can also be used as moulding sand for the preparation of sand moulds for casting, e.g. in the non-bake method.

Thanks to the benchlife extender according to the invention the moulding materials/moulding sands after casting are to the greatest possible extent chlorine-free, so that corrosion of the cast parts is avoided and the used sand cores or moulds can be re-used as used sand. For this purpose the used sand is heat and/or mechanically treated. Both of these treatment methods result in insignificant or no burdening with chemicals that are damaging to health. This re-employment of previously used sand cores or treatment of used sand is ever possible with systems containing bentonite or basic systems.

The invention is explained in more detail by the following examples.

EXAMPLES Example 1 Preparation of a Preferred Phenolic Resin of the Benzyl Ether Type (Precondensate)

In a reaction vessel equipped with cooling, a thermometer and a stirrer:

385.0 PW Phenol 176.0 PW Paraformaldehyde (as the formaldehyde source) and 0.11 PW Zinc acetate were placed. The cooler was set to reflux. The temperature was continuously increased to 105° C. within an hour and maintained at this temperature for between two and three hours until a refractive index of 1.550 was reached.

The cooler was then switched to atmospheric distillation and the temperature increased within one hour to 125 to 126° C., until a refractive index of approximately 1.593 was reached.

Then vacuum distillation took place until a refractive index of 1.612.

The yield was 82 to 83% of the raw materials used.

The phenolic resin was used for the preparation of test specimens according to the cold-box method.

Example 2 Preparation of Cold-Box Phenolic Resin Solutions

From the phenolic resin (precondensate) according to Example 1 once the desired value of the refractive index had been reached, resin solutions for the cold-box method were prepared having the compositions indicated in the following:

Cold-box resin solution AB1

50 PW Phenol resin (precondensate from Example 1) 19 PW Aromatic hydrocarbons with a boiling point of 165 to 180° C. 18 PW DBE (Dibasic Ester) 13 PW Rapeseed oil methyl ester (RME)

Example 3 Preparation of Polyisocyanate Solutions for the Cold-Box Method

According to the invention: Polyisocyanate solutions BB1 to BB6

In each case 100% methane sulfonic acid was used.

Polyisocyanate solution BB1

85 PW Diphenylmethane diisocyanate 12.5 PW Aromatic hydrocarbons with a boiling point of 165 to 180° C. 2 PW Rapeseed oil methyl ester (RME) 0.1 PW Methane sulfonic acid 0.4 PW Water repellent

Polyisocyanate solution BB2

85 PW Diphenylmethane diisocyanate 12.4 PW Aromatic hydrocarbons with a boiling point of 165 to 180° C. 2 PW Rapeseed oil methyl ester (RME) 0.2 PW Methane sulfonic acid 0.4 PW Water repellent

Polyisocyanate solution BB3

85 PW Diphenylmethane diisocyanate 12.3 PW Aromatic hydrocarbons with a boiling point of 165 to 180° C. 2 PW Rapeseed oil methyl ester (RME) 0.3 PW Methane sulfonic acid 0.4 PW Water repellent

Polyisocyanate solution BB4

85 PW Diphenylmethane diisocyanate 12.2 PW Aromatic hydrocarbons with a boiling point of 165 to 180° C. 2 PW Rapeseed oil methyl ester (RME) 0.4 PW Methane sulfonic acid 0.4 PW Water repelient

Polyisocyanate solution BB5

85 PW Diphenylmethane diisocyanate 12.1 PW Aromatic hydrocarbons with a boiling point of 165 to 180° C. 2 PW Rapeseed oil methyl ester (RME) 0.5 PW Methane sulfonic acid 0.4 PW Water repelient

Polyisocyanate solution BB6

85 PW Diphenylmethane diisocyanate 11.6 PW Aromatic hydrocarbons with a boiling point of 165 to 180° C. 2 PW Rapeseed oil methyl ester (RME) 1 PW Methane sulfonic acid 0.4 PW Water repelient

Polyisocyanate solution BB8

65 PW Diphenylmethane diisocyanate 12.8 PW Aromatic hydrocarbons with a boiling point of 165 to 180° C. 2 PW Rapeseed oil methyl ester (RME) 0.2 PW Methane sulfonic acid

Conventionally for comparison: Polyisocyanate solution BB 7

The polyisocyanate solution for comparison BB7 corresponds to solution BB3, with the difference that instead of methane sulfonic acid phosphoryl chloride is used to extend the benchlife.

Example 4 Preparation of Cold-Box Test Specimens and Core Testing of These

-   a) Using the phenolic resin and polyisocyanate solutions indicated     (see Examples 2 and 3) the moulding sand mixtures indicated in the     following Table 1 were prepared, in which

100 PW Quartz sand H 32, 0.7 PW of the respective phenolic resin solution (Example 2) and 0.7 PW of the respective polyisocyanate solution (Example 3) were mixed in a vibratory mixer.

The mixing time was in each case 60 seconds. With the mixtures obtained at a firing pressure of 4 bar, test specimens (+GF+bar) were fired, which were than gasified for 10 seconds at a gasification pressure of 4 bar with dimethylisopropylamine and then flushed with air for 10 seconds. The sand quantify per test specimen was 3 kg, the sand temperature and the ambient temperature were approximately 25° C., the relative humidity (RH) was approximately 39%. Then the flexural strengths of the test specimens obtained in this way were determined according to the GF method. In the preparation of the test as specimens and the testing of the flexural strengths the specifications of VDG leaflet P 73 of February 1996 were applied.

Table 1 provides a comparison of the strength values of six cores according to the invention and a conventional core (in N/cm²).

For the results compiled in Table 1 investigations were firstly performed with a mixture used to prepare a mould test specimen immediately after mixing (“IMMEDIATE” column) and secondly with a mixture first stored for three hours after mixing (for assessing the so-called “benchlife” BL) and then used to prepare a test specimen (“3 HOURS” column).

The results summarised in the following Table 1 show how the test specimens (cores) prepared according to the invention have strength values that are just as good as the cores prepared in the conventional manner.

TABLE 1 Flexural strengths Further processing of the mixture IMMEDIATE 3 HOURS Phenol Poly- Test time resin isocyanate immed. 1 h 24 h immed. 1 h 24 h AB1 BB1 215 328 380 229 329 349 AB1 BB2 224 415 435 230 353 367 AB1 BB3 214 359 417 226 333 353 AB1 BB4 194 338 380 215 326 358 AB1 BB5 200 335 391 216 350 367 AB1 BB6 206 338 388 233 356 370 AB1 BB7 227 385 440 220 351 384 AB1 BB8 220 363 430 223 335 388

Example 5 Preparation of Cold-Box Phenolic Resin Solutions

From the phenolic resin (precondensate) according to Example 1 once the desired value of the refractive index had been reached, resin solutions for the cold-box method were prepared having the compositions indicated in the following:

Cold-box resin solution HA1

55 PW Phenol resin (precondensate from Example 1) 30 PW Tetraethyl silicate 15 PW DBE (Dibasic Ester)

Example 6 Preparation of Polyisocyanate Solutions for the Cold-Box Method

According to the invention: Polyisocyanate solutions HB2 to HB8

Conventionally for comparison: Polyisocyanate solution HB1

Polyisocyanate solution HB1

80 PW Diphenylmethane diisocyanate (MDI) 10 PW Tetraethyl silicate 9.3 PW Dioctyl adipate 0.3 PW Phosphoryl chloride 0.4 PW Water repelient

Polyisocyanate solution HB2

80 PW Diphenylmethane diisocyanate (MDI) 10 PW Tetraethyl silicate 9.5 PW Dioctyl adipate 0.1 PW Methane sulfonic acid 0.4 PW Water repelient

Polyisocyanate solution HB3

80 PW Diphenylmethane diisocyanate (MDI) 10 PW Tetraethyl silicate 9.4 PW Dioctyl adipate 0.2 PW Methane sulfonic acid 0.4 PW Water repelient

Polyisocyanate solution HB4

80 PW Diphenylmethane diisocyanate (MDI) 10 PW Tetraethyl silicate 9.3 PW Dioctyl adipate 0.3 PW Methane sulfonic acid 0.4 PW Water repelient

Polyisocyanate solution HB5

80 PW Diphenylmethane diisocyanate (MDI) 10 PW Tetraethyl silicate 9.2 PW Dioctyl adipate 0.4 PW Methane sulfonic acid 0.4 PW Water repelient

Polyisocyanate solution HB6

80 PW Diphenylmethane diisocyanate (MDI) 10 PW Tetraethyl silicate 9.1 PW Dioctyl adipate 0.5 PW Methane sulfonic acid 0.4 PW Water repelient

Polyisocyanate solution HB7

80 PW Diphenylmethane diisocyanate (MDI) 10 PW Tetraethyl silicate 8.6 PW Dioctyl adipate 1 PW Methane sulfonic acid 0.4 PW Water repelient

Polyisocyanate solution HB8

80 PW Diphenylmethane diisocyanate (MDI) 10 PW Tetraethyl silicate 9.4 PW Dioctyl adipate 0.1 PW Methane sulfonic acid 0.1 PW Phosphoryl chloride 0.4 PW Water repelient

Example 7 Preparation of Cold-Box Test Specimens and Core Testing of These

-   a) Using the phenolic resin and polyisocyanate solutions indicated     (see Examples 5 and 6) the moulding sand mixtures indicated in the     following Table 2 were prepared, in which in each case

100 PW Quartz sand H 32, 0.7 PW of the respective phenolic resin solution (Example 2) and 0.7 PW of the respective polyisocyanate solution (Exemple 3) were mixed in a vibratory mixer.

The mixing time was in each case 60 seconds. With the mixtures obtained at a firing pressure of 4 bar, test specimens (+GF+bar) were fired, which were than gasified for 10 seconds at a gasification pressure of 4 bar with dimethylisopropylamine and then flushed with air for 10 seconds. The sand quantity per test specimen was 3 kg, the sand temperature and the ambient temperature were approximately 25° C. the relative humidity (RH) was approximately 39%. Then the flexural strengths of the test specimens obtained in this way were determined according to the GF method. In the preparation of the test specimens and the testing of the flexural strengths the specifications of VDG leaflet P 73 of February 1996 were applied.

Table 2 provides a comparison of the strength values of seven cores according to the invention and a conventional core (in N/cm²).

For the results compiled in Table 2 investigations were firstly performed with a mixture used to prepare a mould test specimen immediately after mixing (“IMMEDIATE” column) and secondly with a mixture first stored for three hours after mixing (for assessing the so-called “benchlife” BL) and then used to prepare a test specimen (“3 HOURS” column).

The results summarised in the following Table 2 show how the test specimens (cores) to prepared according to the invention have strength values that are just as good as the cores prepared in the conventional manner.

The substantial difference between the conventional core and the cores according to the invention is that in their preparation and also during casting the latter no longer produce any noticeable burden on the workplace. Behaviour during casting has been confirmed by is sample castings performed under laboratory conditions.

TABLE 2 Flexural strengths Further processing of the mixture IMMEDIATE 3 HOURS Phenol Poly- Test time resin isocyanate immed. 1 h 24 h immed. 1 h 24 h HA1 HB1 309 409 453 273 376 401 HA1 HB2 294 397 461 253 335 365 HA1 HB3 283 368 427 244 332 356 HA1 HB4 286 376 429 250 371 394 HA1 HB5 285 353 409 253 367 400 HA1 HB6 280 367 397 245 359 385 HA1 HB7 179 300 329 165 227 250 HA1 HB8 300 418 471 236 365 397 

1. Polyisocyanate component for a moulding material binding agent system, containing at least one sulfonic acid in a solution of at least one polyisocyanate, containing at least two NCO-groups in the molecule, wherein, the sulfonic acid has the general formula R—SO₂—OH, in which R denotes C₁₋₄-alkyl, and the polyisocyanate component contains methylene diphenyl diisocyanate or an oligomer or polymer thereof as polyisocyanate.
 2. Solution containing polyisocyanate, for a moulding material binding agent system, comprising of (a) one or a plurality of polyisocyanates with in each ease two or more NCO-groups in the molecule, wherein the one polyisocyanate or at least one of the plurality of polyisocyanates is a methylene diphenyl diisocyanate or an oligomer or polymer thereof, and (b) one or a plurality of sulfonic acids, wherein the one sulfonic acid or at least one of the plurality of sulfonic acids is selected from the group of sulfonic acids of the formula R—SO₂—OH, in which R denotes an alkyl group with between 1 and 4 carbon atoms.
 3. Solution containing polyisocyanate according to claim 2, comprising of (a) one or a plurality of polyisocyanates with in each case two or more NCO-groups in the molecule, wherein the one polyisocyanate or at least one of the plurality of polyisocyanates is a methylene diphenyl diisocyanate or an oligomer or polymer thereof, (b) one or a plurality of sulfonic acids, wherein the one sulfonic acid or at least one of the plurality of sulfonic acids is selected from the group of sulfonic acids of the formula R—SO₂—OH, in which R denotes an alky group with between 1 and 4 carbon atoms, wherein preferably the one sulfonic acid or at least one of the plurality of sulfonic acids, is methane sulfonic acid, and additionally (c) one or a plurality of (co)-solvents, not selected from the group of ingredients (a) and (b) defined above, and/or (d) one or a plurality of further substances selected from the group consisting of acid chlorides and chlorosilanes and/or (e) optionally one or a plurality of further substances selected from the group of water repellents.
 4. Solution containing polyisocyanate according to claim 2 wherein the solution does not comprise a resin selected from the group consisting of phenolic resins and furan resins.
 5. Solution containing polyisocyanate according to claim 2 wherein the solution comprises no polyol that is suitable for reacting with the polyisocyanate(s) contained, in the solution to form a cold-curing binding agent.
 6. Solution containing polyisocyanate according to claim 2, wherein the solution is either anhydrous or contains water in a maximum quantity that is selected so that the molar ratio of NCO-groups to H₂O is greater than 100:1, preferably greater than 1000:1.
 7. Solution containing polyisocyanate according to claim 2 wherein the solution comprises no moulding matrix.
 8. Polyisocyanate component according to claim 1 for a moulding material binding agent system, comprising 0.01 to 5 wt. %, of the at least one sulfonic acid.
 9. Polyisocyanate component according to claim 8 for a moulding material binding agent system, wherein it contains 55 to 95 wt. %, of the at least one polyisocyanate.
 10. Polyisocyanate component according to claim 1, wherein at least one organic solvent, selected from among tetraalkyl silicate, aromatic hydrocarbons, fatty acid alkyl esters, mixtures of these and mixtures of these with alkylene carbonates or dialkyl esters of aliphatic dicarboxylic acid.
 11. A method of preparing a polyurethane resin, comprising: providing a polyisocyanate component according to claim 1 as a polyisocyanate component of a two-component binding agent system for preparation of a polyurethane resin.
 12. Moulding material binding agent system for preparation of foundry sand cores from a polyol component, containing a solution of a polyol containing phenol with at least two OH groups in the molecule, and a polyisocyanate component, as defined in claim 1, reacting together to form a cold-curing binding agent.
 13. Two-component binding agent system for preparation of a polyurethane resin for casting, comprising of a polyisocyanate component as defined in claim 1 and separately a polyol component, wherein the polyol component preferably comprises a Phenol-formaldehyde resin with two or more methylol groups per molecule.
 14. (canceled)
 15. Mixture for preparation of a core or mould for casting, comprising a moulding matrix and a moulding material binding agent system according to claim
 12. 16. Mould or core for casting, comprising a moulding matrix and the cured binding agent system resulting either from the curing of a moulding material binding agent system according to claim 12 or that can be prepared by moulding a mixture comprising a moulding matrix and the components of a moulding material binding agent system according to claim 12 and curing of the binding agent system in the moulded mixture to form a cured binding agent system.
 17. Method for preparation of a core or mould for casting, with the following steps: mixing a moulding matrix with the components of a moulding material binding agent system according to claim 12, moulding of the resultant mixture comprising moulding matrix and the components of the binding agent system, bringing the resultant moulded mixture into contact with a gaseous catalyst, preferably with a gaseous amine, so that the binding agent system cures and binds the moulding matrix.
 18. A method of extending the benchlife of a mixture, comprising: mixing a sulfonic acid of the general, formula R—SO₂—OH, in which R denotes C₁₋₄-alkyl a moulding matrix and a polyisocyanate component and a polyol component of a two-component binding agent system for preparation of a polyurethane resin for casting, wherein the polyisocyanate component comprises one or a plurality of polyisocyanates with in each case two or more NCO-groups in the molecule, wherein the one polyisocyanate or at least one of the plurality of polyisocyanates is a methylene diphenyl diisocyanate or an oligomer or polymer thereof, and wherein the polyol component comprises a phenol-formaldehyde resin with two or more methylol groups per molecule.
 19. The polyisocyanate component according to claim 1, wherein R is methyl.
 20. The solution according to claim 2, wherein R is methyl.
 21. A solution according to claim 2, comprising a total quantity of sulfonic acid in the range 0.01 to 5 wt. %., in respect of the total weight of the solution.
 22. A solution containing polyisocyanate according to claim 2, comprising a total quantity of polyisocyanate in the range 55 to 95 wt. %, with regard to the total mass of the solution.
 23. A solution containing polyisocyanate according to claims 2, comprising as component (c) one or a plurality of (co-)solvents, selected from group consisting of tetraalkyl silicate, aromatic hydrocarbons, fatty acid alkyl esters (preferably rapeseed oil methyl ester), mixtures of these and mixtures of these with alkylene carbonates or dialkyl esters of aliphatic dicarboxylic acids, preferably dimethyl esters of adipinic acid, glutaric acid and/or succinic acid.
 24. The method according to claim 17, wherein the method is a cold-box casting method. 